Abstract
Studies of the quasi-two-day wave show that it is a summertime phenomenon. In the summer of 1983–84 at Adelaide (35°S, 138°E), the main phase of the wave appeared as a pulse in mid-January which lasted about seven cycles (14 days). Coincident with the onset of the pulse a temporary but substantial change occured in the prevailing circulation throughout a deep layer of the upper mesosphere; a perturbation of more than 10 m s&−1 occurred in the northward flow, whereas the change in the zonal flow (about 30 m s−1 westward) actually caused a reversal of the prevailing eastward simulation above 84 km.
It is suggested that these changes in the prevailing circulation were a response to the wave pulse. A simple calculation is performed to estimate the anticipated response to the observed wave event; under plausible assumptions about the magnitude of mean and eddy dissipation processes, predicted circulation changes agree reasonably well with those observed.
It is concluded that such events have a substantial, if temporary, impact on the prevailing circulation in the upper mesospere and may be important in the transport of atmospheric constituents at these heights during summer.
